Spark plug with single-piece ceramic insulator with tubular portion extending into scavenging chamber

ABSTRACT

A spark plug assembly in which a metallic shell member has an upwardly opening cavity and a downwardly extending hole or opening at the bottom of the cavity, a one-piece insulating member is mounted in the shell member and has an integral, thinwalled tubular portion of relatively small, substantially constant cross-sectional area extending downwardly through the opening of the shell member, and a center electrode means is mounted in a centrally positioned, longitudinally extending opening provided in the insulating member and its downwardly extending tubular portion. The heat range of the plug may be varied by boring a scavenging chamber with a substantially domeshaped upper end and of large cross-sectional area relative to the insulator tip size and of shallow depth relative to other spark plugs in the bottom of the shell member, the depth of the chamber determining the desired heat range.

United States Patent 2,135,624 11/1938 Rabezzana 2,188,166

Emil J. Novak Garden City, NY.

Jan. 8, 1969 Sept. 7 1971 Hamilton-listings Company Ltd. Downsview, Ontario, Canada inventor Appl. No. Filed Patented Assignee References Cited UNITED STATES PATENTS 1/1940 Weinerth.....

2,833,950 5/1958 Hastings 2,906,908 9/1959 Mallory ABSTRACT: A spark plug assembly in which a metallic shell member has an upwardly opening cavity and a downwardly extending hole or opening at the bottom of the cavity, a onepiece insulating member is mounted in the shell member and has an integral, thin-walled tubular portion of relatively small, substantially constant cross-sectional area extending downwardly through the opening of the shell member, and a center electrode means is mounted in a centrally positioned, longitudinally extending opening provided in the insulating member and its downwardly extending tubular portion. The heat range of the plug may be varied by boring a scavenging chamber with a substantially dome-shaped upper end and of large cross-sectional area relative to the insulator tip size and of shallow depth relative to other spark plugs in the bottom of the shell member, the depth of the chamber determining the desired heat range.

momm

SlPAlRIfl PLUG WITH SINGLE-PIECE CERAMIC INSULATOR WITII TUBULAR PORTION EXTENDING INTO SCAVENGING CHAMBER This invention relates to spark plugs for internal combustion engines an more particularly to spark plugs of the general type described in US. Pat. Nos. 2,833,950 and 2,959,703 assigned to the same assignee as the present invention.

These patents disclose a spark plug construction in which the firing tip of the center electrode is enclosed within a thinwalled parallel-sided tubular member of insulating material which extends into a scavenging chamber of relatively wide cross-sectional area, relatively small depth, and substantially dome-shaped upper end thereby to obtain more efficient scavenging, a more rapid heating and cooling of the insulator tip and more uniform temperature of the exposed portion of the tip, and consequently a wider heat range without preignition or fouling. While these features resulted in better performance and longer spark plug life, it has been found that it is still desirable, for best performance, to match the heat range of the plug fairly closely with the motor. It has also been found that certain improvements in the construction of the plug give a stronger product of greater reliability, especially in plugs of higher IMEP. The prior constructions would frequently fail under the temperatures and pressures of modern high compression automotive engines.

An object of the present invention, therefore, is to provide a spark plug assembly having a firing tip of thin-walled insulating material and favorably shaped scavenging chamber which is less likely of mechanical to electrical breakdown than previous plugs of this construction.

A further object is the provision of a spark plug wherein a heat sink material interposed between the insulating member and the metallic shell provides a seal against the entrance of gases therebetween and also provides for better heat transfer and cooling of the firing tip.

A further object is to provide a spark plug in which a relatively sharp-edged annular ridge projects from the base member against the insulating member to assist in sealing against leakage of gases.

A further object is the provision of a method or means whereby the heat range of a given spark plug may be readily varied.

A further object is the provision of spark plugs in which shells and insulating members of a standard size may be readily varied to provide plugs of different heat ranges, i.e. one or, at the most, two insulators will do for all plugs of one thread size.

A further object is the provision of spark plug in which the heat range is varied by the depth of penetration of a thinwalled insulator tip into a scavenging chamber.

In one of its aspects, the spark plug of the invention comprises a metallic shell having an upwardly opening cavity and a downwardly extending opening at the bottom of the cavity. A one-piece insulating member having an integral thin-walled tubular tip portion of relatively small and substantially constant cross-sectional area is mounted in the cavity of the shell with its tubular portion extending downwardly through the bottom opening. The walls could be tapered above the lower opening of the shell. The insulating member is attached to the shell by any desired cementing and sealing compound or mechanical process, and the hole in the shell is of a size only slightly greater than that of the tubular portion to provide good heat transfer therebetween. For example, the size could be 0.005 inch to 0.015 inch greater. A center electrode extends downwardly through the insulating member and its tubular extension and provides a spark gap with a ground electrode carried by the shell. The center electrode and its thinwalled insulating sheath may extend a predetermined distance above or below the bottom of the shell, and a smoothly contoured scavenging chamber of small depth and large cross-sectional area is provided in the bottom of the shell around the center electrode and insulator tip. A heat sink material may be provided between the shell and the insulating member to assist in preventing leakage or passage of gases therebetween and provide for better heat transfer. The shell may also be provided with one or more relatively sharp-edged annular ridges projecting against the insulating member to assist in sealing against leakage of gases.

In another important aspect, the invention provides a method or means for varying the temperature range of a spark plug constructed from shells and insulating members of a standard size. This is accomplished by cutting or otherwise forming the aforesaid scavenging chambers to different predetermined depths, thereby effecting different degrees of extension or protrusion of the thin-walled center electrode into the scavenging chamber. The amount of extension can also be varied by altering the extent to which the insulator tip protrudes past or lies within the steel shell. Thus, spark plugs for engines of various IMElP ratings may be readily assembled or manufactured from a single stock of standardized shells and insulating members, thereby effecting substantial savings in tooling, time, inventory control, and costs.

The above and other objects, features and advantages of the invention will be apparent from the following description and the accompanying drawings which illustrate an exemplary embodiment of the invention.

In the drawings:

FIG. I is a cross-sectional view of a spark plug constructed in accordance with the present invention; and

FIG. 2 illustrates, partly on an exaggerated scale, how the plug of FIG. I can be modified to provide various heat ranges or IMEP ratings.

Referring to FIG. 1 of the drawing, the numeral I0 indicates the usual metallic shell member of a spark plug which has a plurality of wrench engaging surfaces Ill nd external threads 12 adapted to attach the plug to an external wall of an internal combustion engine. The shell 10 is provided with an upwardly opening cavity I3 having a bottom 114i and a recessed seat 15. The shell member is also provided with a hole or opening I6 extending therethrough from the bottom of the cavity 13. A longitudinally extending one-piece insulating member 17 rests upon either the bottom or top seat I5 of the shell and is securely attached thereto by a suitable sealing compound or process as well known in the art. The insulating member 17 is provided with an integral thin-walled tubular tip portion 13 of relatively small and substantially constant cross-sectional area which extends downwardly through. the opening 16 in close approximity thereto to provide good heat exchange therebetween, i.e., the opening is of a size only slightly greater than that of the tubular portion to produce a relatively close fit between the same. A center electrode comprising conductors I9 and 20 joined together by a conducting glass seal 21, also well known in the art, is positioned and sealed into a coaxial opening provided in the insulating member I7 and its tubular extension I8 and cooperates with a ground electrode 22 carried by the shell 10 to provide the usual spark gap. A lip portion a or shell 10 is adapted to be crimped over the thickened portion 17a of the insulating member I7 and assists in securing the insulator to the shell in a sealed relationship. The seal is immeasurably improved by a well-known process known as hot upset" in which an electric current heats the thin section in the shell while crimp in pressure is applied. Current is turned off before crimping pressure is released. Shrinkage keeps seal tight.

In order to further seal the joint between the shell 10 and the insulating member I7 and at the same tim provide good heat transfer between the same, a heat sink material 23 may be provided in the space between the opening 16 and the tubular insulator portion 18 where a large part of the heat transfer and cooling of the tip 18 occurs. Such heat sink, for example, may comprise, among others, a material known under the trade name of Dow Corning 340 Silicone Heat Sink Compound," and provides a longlasting seal with high thermal conductivity. This seal would be used primarily in plugs of higher IMEP (over 250 for example) and is primarily for the purpose of preventing the entrance of hot combustion gases into the space between the insulating tip and the shell at the opening 16, such gases interfering with heat transfer and the proper cycling of the insulator tip temperatures.

in order to further to seal the joint between the shell and insulating member to prevent leakage or passage of gases therebetween, the bottom 14 of shell may also be provided with a relatively sharp-edged annular ridge 24 which projects against the insulating member 17 and is partially crushed during the crimping operation to provide a seal between the insulator and the steel shell and takes the place of a gasket. Alternatively, a similar ridge 25 may be provided on the seat 15.

The thin-walled insulating tube 18 may extend to, i.e., terminate at, a predetermined distance within or beyond the threaded end of the shell 10 (from 0.075 inches within to 0.125 inches beyond the end of the shell, for example), and a smoothly contoured scavenging chamber 26 of shallow depth and large cross-sectional are relative to the tubular tip 18 is usually provided in the bottom of the shell 10.

The structure thus far described causes the tubular firing tip to heat up faster than conventional plugs during rapid acceleration, thus reducing lead oxide deposits which cause misfiring of the plug. it also causes the insulator tip more nearly to approach the ideal temperature range of 650 C. to 750 C. throughout the entire speed and power range of the engine, and provides a more uniform temperature throughout the length of the insulator tip which means that the base of the tip remains above the critical temperature for fouling even when the engine is idling or not yet warmed up. This permits the use of a cooler running plug whereby the lower than normal temperature of the insulator tip and electrodes reduces a gap wear and degeneration of the insulator tip.

The favorably shaped scavenging chamber promotes more complete elimination of exhaust gases from the vicinity of the insulator tip and electrodes gap. in addition to reducing fouling, this ensures a fresher fuel/air mixture which ionizes more readily than a mixture of exhaust and new gases and thus promotes more consistent firing. This means better fuel economy, more power and less air pollution.

As above set forth, one of the important aspects of this invention is the provision of a method or means by which the heat range of spark plugs assembled or constructed from shells and insulating members of a standard size for plugs of a given thread size may be readily and economically varied thereby to provide plugs for engines of different IMEP, up to at least 250-260 IMEP, from a stockpile or inventory having fewer parts of different size. As illustrated in FIG. 2, this comprises the boring (which term is intended to mean drilling or otherwise forming) the scavenger chamber 26 of FIG. 1 to different predetermined depths as indicated by the dashed lines 27, 28, 29, and 30. insulating tips 18 of a predetermined given length thus protrude different distances into the firing part of the engine cylinder and adjust or vary the plug for engines of different IMEP rating. For insulating tips of a given length, i.e., tips terminating a predetermined distance above or below the bottom of the shell member, the IMEP varies approximately inversely with the depth of the scavenging chamber.

The above-described heat sink" is unnecessary for plugs having an IMEP rating of 250-260 or lower, and may be omitted on plugs of higher rating. For engines of higher IMEP (above 250-260 lMEP,vfor example) it may be desirable or necessary to shorten the tip length and increase the length of the middle step. For engines of very high rating (above 340 IMEP, for example), the scavenging chamber may be entirely omitted, the protrusion of a very small portion of the center tip beyond the bottom of the shell member (because it is maintained within the ideal temperature limits), this sufficient to effect proper operation of the engine and scavenging of the insulator tip and electrodes.

While an exemplary embodiment of the invention has been described an illustrated, it will be apparent that alterations, changes and modifications may be made therein without departing from the spirit of the invention, an it is intended to be limited only by the scope of the appended claims.

What is claimed is:

l. A spark plug assembly comprising a metallic shell member having an upwardly opening cavity and an opening extending downwardly therethrough from the bottom of said cavity, a scavenging chamber extending downwardly from said opening, a one-piece ceramic insulating member sealingly mounted in said cavity and having an integral thin-walled tubular portion which is of relatively small substantially constant cross-sectional area throughout the length of said tubular portion from where it emerges from said opening and extends downwardly therefrom and into said scavenging chamber, said scavenging chamber being of relatively small depth and large cross-sectional are relative to said tubular portion of the insulating member, said opening being of only slightly larger crosssectional area than said downwardly extending tubular portion to assist in heat transfer therebetween, and center electrode means extending through a coaxial opening provided in said insulating member and its tubular portion, said tubular portion extending a predetermined distance downwardly beyond the top of said scavenging chamber to control heat range.

2. A spark plug assembly as defined in claim 1 in which the scavenging chamber is substantially dome-shaped at its inner end adjacent said opening at the bottom of said shell member.

3. A spark plug assembly as defined in claim 1 in which the bottom of the cavity in said shell member provides a seat for said insulating member, and said seat has an outwardly extending, relatively sharp-edged annular ridge spaced from the edge of said seat and projecting against the insulating member to provide a gasket to assist in sealing the members against leakage of gases therebetween and to assist in heat transfer therebetween.

4. A spark plug assembly as defined in claim 3 in which said shell member is provided with a second internal seat for supporting said insulating member, and said second seat is provided with an outwardly extending, relatively sharp-edged annular ridge spaced from said second seat and projecting against the insulating member to provide a sealing gasket.

5. A spark plug assembly as defined in claim 1 wherein the scavenging chamber has walls that are substantially parallel to the exterior walls of said tubular portion extending into said chamber.

abcve-identified patent as 5 below howw CERTHICATE i CGELRECTEON Patent N0. 1, ,6O3JSQBQ Inventor(s) Emil J.

It is certified that error appears in the and that said Letters Patent are hereby correc 

1. A spark plug assembly comprising a metallic shell member having an upwardly opening cavity and an opening extending downwardly therethrough from the bottom of said cavity, a scavenging chamber extending downwardly from said opening, a onepiece ceramic insulating member sealingly mounted in said cavity and having an integral thin-walled tubular portion which is of relatively small substantially constant cross-sectional area throughout the length of said tubular portion from where it emerges from said opening and extends downwardly therefrom and into said scavenging chamber, said scavenging chamber being of relatively small depth and large cross-sectional are relative to said tubular portion of the insulating member, said opening being of only slightly larger cross-sectional area than said downwardly extending tubular portion to assist in heat transfer therebetween, and center electrode means extending through a coaxial opening provided in said insulating member and its tubular portion, said tubular portion extending a predetermined distance downwardly beyond the top of said scavenging chamber to control heat range.
 2. A spark plug assembly as defined in claim 1 in which the scavenging chamber is substantially dome-shaped at its inner end adjacent said opening at the bottom of said shell member.
 3. A spark plug assembly as defined in claim 1 in which the bottom of the cavity in said shell member provides a seat for said insulating member, and said seat has an outwardly extending, relatively sharp-edged annular ridge spaced from the edge of said seat and projecting against the insulating member to provide a gasket to assist in sealing the members against leakage of gaSes therebetween and to assist in heat transfer therebetween.
 4. A spark plug assembly as defined in claim 3 in which said shell member is provided with a second internal seat for supporting said insulating member, and said second seat is provided with an outwardly extending, relatively sharp-edged annular ridge spaced from said second seat and projecting against the insulating member to provide a sealing gasket.
 5. A spark plug assembly as defined in claim 1 wherein the scavenging chamber has walls that are substantially parallel to the exterior walls of said tubular portion extending into said chamber. 